Isolating circuit



Feb. 22, 1955 F. P. ZAFFARANO 2,702,856

' ISOLATING CIRCUIT Filed Feb. 19, 1946 CONTROL VOLTAGE {a STIR: NEGATIVE VOLTAGE SUPPLY3 PLATE VOLTAGE SUPPLY TRIGGER OUTPUT TRIGGER INPUT INVENTOR.

FRANK P. ZAFFARANO ATTORNEY United States Patent M ISOLATING CIRCUIT Frank P. Zafiarano, Boston, Mass., assignor, by mesnc assignments, to the United States of America as represented by the Secretary of the Navy Application February 19, 1946, Serial No. 648,792

5 Claims. (Cl. 250-27) This invention relates to floating grid electron tubes and more particularly to floating grid triodes used as circuit isolating elements.

Circuit isolating elements as previously known in the art have most commonly had a nxed value of impedance. For applications requiring a variable impedance isolating element, the internal plate impedance or electron tubes connected in the conventional manner have been used. To obtain the Iull range of impedance change t'rom an electron tube so connected it was necessary to vary the control voltage applied to the control grid over an extremely wide range so as to change the tube from a completely cut-on condition to a completely conducting state. ln this invention, the above-mentioned changes in impedance are obtained from a floating grid triode by means of small changes in voltage on the grid of a control tube. One specific application of such a variable resistance isolating element is found in a biased multivibrator gate generator with a variable gate length.

A primary ob ect of this invention is to provide a circuit isolating element having a variable impedance.

Another object of this invention is to use a floating grid tube as a circuit isolating element.

Another object is to provide a floating grid triode as a circuit isolating element with a control electron tube to cause variation of the internal plate impedance of the floating grid electron tube.

A further object is to provide a biased multivibrator gate generator having a gate length dependent upon the magnitude of a control voltage.

These and other objects will be apparent to those skilled in the art from the following description when taken with the accompanying drawing which is a schematic diagram of one embodiment thereof.

Referring to the drawing, an input trigger voltage applied to terminal 11 is coupled capacitively through condenser 12 to the cathode of diode electron tube 13. The cathode of diode 13 is connected through resistor 14 to a source of positive voltage at terminal 15. The plate of diode 13 is coupled directly to the plate of triode electron tube which is the normally non-conducting tube of a biased multivibrator. The plate of triode 20 is also connected through resistor 21 to the plate voltage supply at terminal 15, and through condenser 22 to the grid of triode electron tube 23. The grid of triode 20 is connected to a negative voltage supply at terminal 25 through resistor 26, and to the plate of triode 23 through the parallel combination of condenser 27 and resistor 28. The plate of triode 23 connects through resistor 30 to the plate voltage supply at terminal 15 and its cathode is grounded. The grid of triode 23 is also connected to ground through resistor 31, and to the cathode of triode electron tube 32. The plate of triode 32 connects directly to the plate of triode electron tube 33, and the grid of triode 32 has no connection. The plate of triode 33 connects through plate load resistor 34 to the plate voltage supply at'terminal 15, and the cathode is grounded. The grid of triode 33 is connected to the negative voltage supply at terminal 25 through resistor 35 and to the slider of potentiometer 36 through resistor 37. The resistance strip of potentiometer 36 connects between ground and the control voltage supply at terminal 38. In this embodiment an output is obtained from the plate of triode 20 by means of a capacitance coupling through condenser 40 to output terminal 41.

The circuit as shown will produce output voltage gates having a time duration of approximately 200 microsec- 2,702,856 Patented Feb. 22, 1955 onds, which gate duration may be increased rapidly to approximately 1500 microseconds by a relatively small change in the control voltage apphed at terminal 38. The operation of the circuit to provide these outputs may be explained as follows. A negative trigger voltage input is apphed to terminal 11 and througn condenser 12 to the cathode of diode 13. With triode 20 non-conductmg the negative trigger voltage will be passed by diode 13 and applied through condenser 22 to the control grid of normally conducting triode 23. This trigger voltage initiates the multivibrator action which results in triode 23 being cut-oil and triode 20 being brought into conduction. The duration of this part or the multivibrator cycle, and hence the duration or the output voltage gate is substantially determined by the time constant for charging condenser 22 through the effective resistance in series therewith. If the control voltage applied at terminal 38 is such that triode 33 is non-conducting the voltage at the plate of triode 32 will be high and all electrons emitted by the cathode of triode 32 will be drawn to the plate resulting in a low internal impedance for triode 32. This efiectively places resistor 34 in parallel with large resistor 31 and results in a short time constant for charging condenser 22. As the control voltage at terminal 38 is increased to a value such that triode 33 begins to conduct the potential at theplate of triode 33 and hence at the plate of triode 32 will drop rapidly due to current drawn by triode 33 through resistor 34. As the plate voltage of triode 32 reaches a low value the electrons emitted from the cathode tend to collect on the floating control grid and will repel other electrons which might otherwise pass through to the plate. This effectively cuts oil all electron flow through triode 32 causing it to have a very high internal impedance. The time constant for charging condenser 22 then is determined substantially by the resistance of resistor 31, resulting in an output voltage gate of considerably increased duration. In this manner the internal impedance of floating-grid triode 32 is used as a variable isolating impedance to change the time constant of the grid circuit of multivibrator tube 23.

During the conducting period of triode 20 the multivibrator is efiectively isolated from input terminal 11 by diode 13. With triode 20 conducting the plate of diode 13 is at a lower potential than its cathode blocking the passage of any trigger voltages, either positive or negative to the multivibrator circuit.

The invention described in the foregoing specification need not be limited to the details shown, which are considered to be illustrative of one form the invention may take. The scope of the invention is defined by the appended claims.

What is claimed is:

1. A variable resistance circuit-isolating element comprising a first electron tube having at least a cathode, an anode, and a floating control grid, the anode to cathode resistance of said first tube constituting said variable isolating resistance, a second electron tube having at least a cathode, an anode, and a control grid, a source of anode supply potential, means for returning the anode of said second tube to said source of anode supply potential, means for applying a variable control voltage to the control grid-cathode circuit of said second electron tube, means for electrically coupling the anodes of said electron tubes, and means for electrically coupling the cathodes of said electron tubes.

2. A variable resistance circuit-isolating element COI'Ilprising a first electron tube having at least a cathode, an anode, and a floating control grid, the anode to cathode resistance of said first electron tube being dependent upon the difference in potential between said anode and said cathode, the anode to cathode resistance of said first tube constituting said variable isolating resistance, a second electron tube having at least a cathode, an anode, and a control grid, said anode of said second tube being connected directly to said anode of said first tube, a resistor connected between said cathode of said first tube and a point of fixed potential, said cathode of said second tube being connected directly to said point of fixed potential, a source of anode supply potential, an anode load impedance returning said anodes to said source of anode supply potential, and means for applying a variable control voltage to the control grid-cathode circuit of said second electron tube.

3. An unsymmetrical multivibrator gate generator having a variable gate comprising first and second electron tubes each having at least a cathode, an anode, and a control grid, a resistance-capacitance coupling between the anode of each of said electron tubes and the control grid of the other tube, said first tube being normally non-conducting and said second tube being normally conducting, a third electron tube in the form of a diode having an anode and a cathode, said anode of said diode being connected to said anode of said first tube, means for applying negative trigger pulses to said grid of said second tube through said diode and said coupling between said anode of said first tube and said grid of said second tube for rendering said second tube non-conducting and rendering said first tube conducting, said diode blocking all negative input pulses during the conduction of said first tube by virtue of the decreased potential at said anodes of said first tube and said diode, a fourth electron tube having at least an anode, a cathode, and a floating grid, a fifth electron tube comprising at least an anode, a cathode, and a control grid, said anodes of said fourth and fifth tubes being directly connected, said cathode of said fourth tube being returned to said control grid of said second tube, a source of anode supply potential, a load impedance, said anodes of said fourth and fifth tubes being returned to said anode supply potential through said load impedance, the internal cathode to anode resistance of said fourth tube constituting a part of the total effective resistance in said resistancecapacitance coupling between said grid of said second tube and said anode of said first tube, and means for applying a source of control voltage to the control grideathode circuit of said fifth tube, the magnitude of the internal resistance of said fourth tube being dependent upon the magnitude of said control potential.

4. In an electrical circuit, apparatus for varying the effective impedance between a first point and a point of reference potential comprising, a resistor connected between said first point and said reference potential point, a source of potential positive with respect to said reference potential point, a first electron tube having at least an anode, a control grid, and a cathode, said cathode being connected to said reference potential point, an anode load impedance returning said anode to said positive potential source, a second electron tube having at least an anode, a floating control grid and a cathode, said cathode of said second tube being connected to said first point, means connecting the anodes of said first and second tubes, and means for varying the control grid to cathode potential of said first electron tube.

5. An unsymmetrical multivibrator gate generator having a variable gate comprising, first and second electron tubes each having a cathode, an anode, and a control grid, resistance-capacitance coupling between the anode of each of said electron tubes and the control grid of the other tube, said first tube being normally non-conducting and said second tube being normally conducting, means for applying negative trigger pulses to the grid of said second tube for rendering said second tube nonconducting and said first tube conducting, a third electron tube having at least an anode, a cathode and a floating control grid, a fourth electron tube having at least an anode, a cathode and a control grid, means directly connecting the anodes of said third and fourth tubes, means directly connecting the cathode of said third tube to the control grid of said second tube, a source of anode potential, a load impedance, the anodes of said third and fourth tubes being returned to said anode potential through said load impedance, the internal cathode to anode resistance of said third tube constituting a part of the total effective resistance in said resistance-capacitance coupling between the grid of said second tube and the anode of said first tube, and means for applying a source of control voltage to the control grid-cathode circuit of said fourth tube, the magnitude of the internal resistance of said fourth tube being dependent upon the magnitude of said control potential.

References Cited in the file of this patent UNITED STATES PATENTS 1,934,322 Osbon Nov. 7, 1933 2,212,645 Morton Aug. 27, 1940 2,265,290 Knick Dec. 9, 1941 2,390,608 Miller et al Dec. 11, 1945 2,432,204 Miller Dec. 9, 1947 

